1. Field of the Invention
The invention relates to a method for the control of an articulated or toggle-lever press and an articulated or toggle-lever press controlled by the method.
2. Discussion of Prior Art
Such methods are used in particular in cutting and forming presses of modern design with hydromechanical toggle-lever drives. The Applicant has successfully introduced into the market, for example under the name differential travel press (DTP), a toggle-lever sheet metal cutting press which is described, for example, in German Patent Document 2925416 or EP-A1 250610. The descriptions and drawings in the above identified Patent Documents of the parts toggle-lever arrangement (individual or a plurality in parallel) and support thereof on the press frame and support of the working cylinder on the press ram are regarded as being disclosed herein for the purpose of the design of an embodiment.
Such a press has two toggle lever systems whose toggle joints bend outward toward the center of the press which are activated by a piston rod of a cylinder/piston arrangement arranged symmetrically with respect to the toggle levers, during a cycle in the forward direction and subsequently in the backward direction. The market is also familiar, although to a lesser extent, with a press which was introduced as a differential pressure press (DPP) and has a further rod system guided in roller rails, between the piston rod and the coupling points on the toggle levers. Such a press was presented to the public in August 1987 and subsequently brought into use.
The origins of both known presses are to be found in a toggle-lever press having a crank drive which operated the toggle levers in order further to reduce the velocity of the press ram in the region of the bottom or upper (depending on whether the working region was at the bottom or top) dead center and to keep it as slow as possible over a certain period or over a certain distance. This is because it was possible to achieve more precise cutting or machining quality when cutting or stamping or drawing the material to be machined, than in the case of a straight-forward crank drive without intermediate toggle levers. In addition, it was possible correspondingly to increase the force in the working range (cutting range) by means of the transmission effect of the toggle levers.
The toggle levers also ensure in particular the precision in the cutting direction (cutting depth), which was also utilized, inter alia, in the case of the toggle-lever presses with a hydraulic piston drive, as shown, for example, in GB-A 707815.
Although attention was focused earlier in particular on obtaining the stated velocity reduction in the working range and subsequently on improving the cutting precision, with increasing automation of the production processes the working velocity (number of strokes) as well as very high precision were forced into the forefront. The differential travel press achieved this through a combination of the advantages of an eccentric press (rapid continuous running) with those of a hydraulic press (pressure control and velocity variation) and those of a toggle-lever press (high forces in the working range and very high precision with regard to the cutting depth). The differential pressure press subsequently constructed on the basis of the differential travel press attempted to increase the number of strokes of the press by additional mechanical means comprising roller rails and an intermediate rod system, or this was achieved in an expensive manner by means of the additional components subjected to considerable wear.